Thomas and Frances' eldest son, Thomas II, was born in 1640 in Windsor, Connecticut Colony. On April 1, 1663, at the age of twenty-three, he was married to Constant Hawes, daughter of immigrants Richard and Ann Hawes of Dorchester.

Thomas II was a miller and a farmer in the Little River District of Windsor. As late as January 1660, Thomas II is listed as sitting in the "long seats" in the Windsor meeting house.

In April 1667 these lands were laid out on the south side of the Westfield River and referred to as "Dewey's Meadows." It was confirmed in Jan. 1668 with Thomas II being the sixth settler on Main Street in Westfield. From then on he became an influential citizen and was ordered by the settling committee to review the land to be fenced and determine where the fences were to be set and where each man's property shall be. He was also commissioned to determine the boundary line between Springfield and Westfield.

Thomas Dewey II had an account at the only store in the area that was owned by John Pyncheon. The following is copied from an original record book of this store:

In the year 1772, a second mill in town was completed two miles from the center of town on Two-Mile Brook in the Little River District by Joseph Whiting and three Dewey brothers, Thomas II, Josiah and Jedidiah. Later that year the town council agreed to allow them to keep a toll of 1/12 of the corn they ground. They also granted the four men ten acres each, totally forty acres of land around the mill, taking in the land where the water is ponded for the mill. Later in 1676, Thomas Whiting sold out to the brothers.

The Deweys were sued by five of the settlers for unlawfully keeping a dam on the Two-Mile River. They lost but appealed the decision. The records mention that it was quite a court battle and some shady dealings by one of the plaintiffs were suspected.

Thomas II was a representative to Boston from 1677 to 1679, a Selectman in 1677 and 1686. In September 1676 he was licensed by the Court to keep a "Publique House of Entertainment" and in 1680 he took the Freeman's Oath. Soon after this date he received another appointment, this time he was to form a committee to locate the country road to Windsor. He was appointed Cornet of the Hampshire Troops of the General Court in July 1685. Thomas Dewey II had joined the Westfield church in May 1680.

He and Constant raised a family of six boys and four girls. The children were Thomas Jr., Adijah, Mary, Samuel, Hannah, Elizabeth, James, Abigail, James, Israel and Eleazor.